This invention relates to an apparatus for removing a quantity of semi-conductor wafers, glass photomask plates, or the like, from a first wafer boat and replacing them into a second wafer boat. The term "wafer" as used herein is to be considered synonymous with any thin, flat planar material requiring delicate handling in a clean environment.
In the manufacture of integrated circuits, semi-conductor wafers or substrates from which the chips are cut are processed through a large number of steps. The basic material for the substrate of the wafer may be silicon, glass or ceramic materials of various sorts. In a number of separate and distinct processing steps, this substrate, or wafer, is subjected to coating, etching, cleaning, and testing. Such steps are most advantageously carried out with multiple wafers, rather than processing individual wafers. Therefore, such wafers are typically processed in groups of about twenty-five, and are assembled in "boats". Such boats are the conventional means of transporting wafers, and for holding wafers during processing, and may be made of metal, plastic, teflon, etc. Frequently, successive steps in the processing require that the wafers be transferred to a different type of boat, as one boat may be sensitive to a particular processing step while another type is not.
Therefore, machines have been developed which will remove all of the wafers from a first boat and transfer them to a second boat. However, such machines heretofore have operated by activating various components in the machines with pressurized air or inert gas. The problem which arises with prior art machines is that, since moving parts are required, contamination from wear of such parts is always a possibility. Furthermore, if the seals between the pressurized components and the ambient room within which the wafers are being processed wears or fails, the pressurized gaseous medium can "blow-by" the damaged seal, further contaminating the wafers and the air of the clean room within which the process is proceeding.
The present invention provides an apparatus and method for transferring wafers without the possibility of blow-by contamination resulting from the use of pressurized air. The principal of the present invention is that negative pressure can cause movement of machine parts, just as pressurized air can. Therefore, by utilizing negative pressure induced by vacuum to move machine parts, lower pressures (and therefore less expensive equipment) are necessary, smoother part movement may be obtained, and even if wear is experienced, contamination of the wafers or clean room will not be experienced.
Therefore, it is an object of the present invention to provide an apparatus, and a method, utilizing negative pressures, to automatically remove a plurality of wafers from a first boat and transfer them to a second boat.